Cylinder Head Fundamentals Flashcards
What 2 materials are used for cylinder heads?
Cast iron alloys
Aluminum
What factors influence the design of a cylinder head?
Engine application
Horsepower rating
max RPM
Method of induction
Four-valve cylinder heads offer increased:
Volumetric efficiency
Turbulence
Injector tube
Copper, stainless, ar brass sleeve pressed into the head. Usually surrounded by coolant to cool injector during operation
There must be a seal between the injector tube and head to prevent?
Coolant from leaking past the tube into the combustion chamber and the crankcase,
Combustion from leaking past the tube into the cooling system
Coolant and Lube passages
Coolant is routed through head near high heat areas.
Oil is routed from the main gallery in the block to lubricate and cool the valve operating mechanisms
Valves preform two basic functions:
Open and close the cylinder to allow airflow during the intake and exhaust events
Seal the cylinder during the compression and power events
Valve lock groove
Groove machined into the valve stem and mates with a lug on the valve locks. The valve locks and retainer keep the valve and valve spring together
Valve stem
is the main shaft that supports the valve head. The stem fits inside valve guide in the cylinder head
Valve Fillet
Area between the stem and the head, is a smooth radius for strength and stress relief. the radius also enhances air flow.
Valve Face
Is a smooth, machined surface that mates with the valve seat in the head
Valve margin
Is the material between the valve face and valve head. The margin supports the valve face and provides material for heat absorption. Valve should be replaced when margin is 1/2 gone
Valve Head
lower end the is exposed the the combustion chamber. size of valve is determined by the diameter of the head
Valve Tip
The part of the valve that is in contact with the valve operating mechanism
One piece valve
Used when a single metal alloy can be used to provide all the qualities required for valve construction
Two-piece valve
Allow the stem and head to be constructed of different materials. The stem must be made of a metal alloy that resists scuffing and scoring. The head must be resistant to extreme heat, pressure and corrosive gases
Solid stem valve cooling
Approximately 75% of cooling occurs between valve face and valve seat, 25% is transferred from valve stem to valve guide.
Sodium cooled exhaust valves
Used in severe duty applications where additional valve cooling is required. When valve heats up sodium in stem tuns to liquid acts like a shaker moving more heat out through the stem
Valve seat
Sealing point between valve face and the cylinder head. Can either be integral or replaceable. Replaceable inserts are made from hardened alloy such as Stellite.
Valve face to seat contact is necessary to:
Create an effective combustion chamber seal
Allow proper valve cooling
Valve guides
Supports the valve to keep it square with the valve seat. Can be either integral part of head, or replaceable. Replaceable ones are made out of material that has better wear characteristics then cast iron.
Single coil valve springs
Single coil spring usually have a flat inner damper coil to counteract valve spring vibrations at higher RPM’s.
Single coil springs can be either constant rate or progressive rate
Dual coil spring assemblies
Have and inner and outer coil, used to increase the amount of valve spring tension over single valve springs.
Spring seat
hardened washer installed under each spring to: help locate the valve spring and keep it centred over the guide, prevent erosion of the casting by keeping the spring from contacting the cylinder head material
Valve retainers and locks
Retainer forms a top to keep the valve and spring as a unit, Inside bore of the retainer is tapered to match the outside of the locks.
Valve seals
Positive seals: fits down over the stem and provide best control of stem lubrication
Non-positive: Acts like shield or deflector t divert the splash oil away from the valve guide and stem
Rocker Arm tip contact surface
the point of the rocker arm that contacts the tip of the valve stem
Rocker arm adjusting screw
provides a means for adjusting clearance in the pushrod operating mechanism
Rocker arm bushing
a replaceable wear surface between the rocker arm and the shaft
Rocker arm ratio
Ration that increases the valve opening compared to the actual amount of cam lobe lift
Valve bridges
Also called valve crossheads, used on cylinder heads with four valves. the bridge spans a pair of common valves and allows one rocker arm to open both valves simultaneously
What are 2 types of head gasket construction?
Steel
composition
Head gasket design
Categorized as being one-piece or multi-piece. Engine design, horsepower rating, application are all factor that influence the type of gasket used
The most common material used for diesel engine cylinder head construction is:
Cast iron alloy
List two main benefits of a four-valve head over a two-valve head?
Increased volumetric efficiency
Increased turbulence
What are the purpose of ports in the head?
Direct airflow in and out of the cylinder
Why must there be a seal between the cylinder head and an injector tube?
Prevent coolant from leaking past the tube into the combustion chamber
Prevent combustion from leaking past the tube into the cooling system
Explain why an exhaust valve is usually made of higher quality material than an intake valve?
It operates with higher temperatures and more corrosive gases
the purpose of a carbon scraper on a valve is to prevent carbon buildup:
In the lower part of the valve guide
2 benefits of having valve equipped with rotators?
Rotation provides a changing wear surface for more even valve and seat wear
Rotation creates wiping action that helps keep the valve face and seat clean of carbon
